Bathtub mat



FIG. 1 is a top perspective view of a design for a bathtub mat;

FIG. 2 is a top perspective view thereof;

FIG. 3 is a bottom perspective view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a side view thereof; and,

FIG. 6 is a bottom view thereof. 

CLAIM The ornamental design for a bathtub mat, as shown and described. 